There is conflicting evidence as to the role of mesoderm and ectoderm in early odontogenesis. It is proposed to investigate the reasons for these differences by culturing 11-14 day post-conception mouse tooth germs, which will be recombinations of tissues separated by several different enzyme techniques, on the chick chorioallantois. The resulting morphologic features will indicate whether different separation techniques did influence the previous results and will also indicate that at certain stages of interaction morphogenic information may be intercellular in location. TEM studies of the tissues at various stages of separation will be made. The inductive role of the dental lamina will be investigated by transplanting the most distal tooth germ at a particular stage, and its attendant distolingual lamina, when there are still more tooth germs to differentiate. Both contralateral dental sites and ectopic subcutaneous sites will be used to test the interaction of ectoderm and native, but not contralateral mesoderm, or totally foreign mesoderm. The readily accessible pouch embryos of Didelphis marsupialis will primarily be used as well as a totally extraoral technique which will not interfere too greatly with the suckling and attachment mechanisms. The differentiation of odontoblasts from bovine pulp cells separated into layers enzymatically and grown in organ culture will be studied to establish what proportion of these cells have this potential and what cells and other substances will induce this reaction.